Intramuscular fat infiltration is associated with higher vertebral void space burden and lower volumetric bone...

Ectopic fat infiltration is increasingly recognized as an important determinant of musculoskeletal health, but its relationship with localized vertebral trabecular deterioration remains unclear. This study aimed to investigate the associations of regional adipose tissue distribution, particularly intramuscular fat infiltration, with vertebral void space burden and volumetric bone mineral density (vBMD) using quantitative computed tomography (QCT).

This cross-sectional study included 327 postmenopausal women and men aged ≥ 50 years who underwent QCT. Visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT), intermuscular adipose tissue (IMAT), and intramuscular fat fraction (IMFF) were quantified. Vertebral void space burden was assessed by void space volume (VS) and void space volume ratio (VS/TV), alongside vBMD. Multivariable linear regression, restricted cubic spline, subgroup, and sensitivity analyses were performed.

Higher IMFF and IMAT were significantly associated with greater vertebral void space burden. Each 10-percentage-point increase in IMFF was associated with 257.2% higher VS and 251.8% higher VS/TV; these associations remained significant after additional adjustment for vBMD, indicating partial independence from average trabecular density (VS: 90.5%; VS/TV: 88.2%; all P < 0.001). Each 1-SD increase in IMAT was also associated with higher VS and VS/TV, independent of vBMD. Both IMFF and IMAT were inversely associated with vBMD.

Intramuscular fat infiltration was independently associated with greater vertebral void space burden and lower vBMD, suggesting that ectopic muscle fat may provide complementary imaging information on localized vertebral structural deterioration beyond conventional density-based measures. Intramuscular fat infiltration was associated with greater vertebral void space burden and lower volumetric bone mineral density on QCT. Ectopic muscle fat may provide complementary imaging information on localized vertebral trabecular deterioration beyond average bone density alone.